Every PO car was, at least once, available to non pre-order players, and should therefore be available again. But some of them were not seasonal championship or percentage rewards, so they don’t seem likely to be available that way in repeat seasons.
Can we get a Forzathon Shop event? The AM DB11PO was only ever offered once, via the shop.
The PO cars are not possible to list in the auction house, so those who do have them cannot sell.
If these cars had only ever been available via pre-order, I would not have made this suggestion. But all of them are either currently available (via Eliminator, for example) to earn, or are gifted to all players, or have been otherwise available by purely in-game means.
There is a declaration on the forzasupport site that every car that has been available, will be available again.
It’s past time for that to be true.